The present invention relates to a filter for a cigarette, and a filter-tipped cigarette using the filter.
A cigarette filter is known which has a central axial extending passage therethrough, or which has a plurality of axially extending passages at or in the peripheral portion thereof.
In use, such a filter delivers part of the smoke of the cigarette directly to the smoker through the passage(s). This non-filtered smoke locally spreads in the smoker""s mouth, and the smoker can therefore enjoy not only a mild smoking feeling but also the original aroma or flavor of the cigarette, provided that there is an appropriate ratio of the quantity of non-filtered smoke directly delivered to the smoker through the passage(s) to that of filtered smoke delivered to the smoker through a filter material.
This ratio of smoke quantities is greatly influenced by the size of the central passage (or the number and arrangement of the peripheral passages) and the axial air-flow resistance of the filter material. It is therefore desirable to facilitate control of the this ratio. Especially, the quantity of non-filtered smoke directly delivered to the smoker is important for providing the original taste and aroma of the cigarette to the smoker.
The non-filtered smoke in the passage(s) may be diluted by ventilation air introduced from outside to give a milder smoke. However, it is difficult to introduce such ventilation air into a central passage. In a filter having passages located at or close to the outer peripheral surface of the filter, ventilation air from outside can be introduced directly into the passages. In this filter, however, the direct introduction of the ventilation air is apt to alter extremely the axial air-flow resistance of the filter and to give a poor smoking result it is difficult to control precisely the amount of ventilation air (and hence diluting ratio of the non-filtered smoke) whilst keeping the axial air-flow resistance of the filter within a desired range.
The first object of the present invention is to provide a filter for a cigarette and a filter-tipped cigarette which are appropriate for controlling the ratio of the quantity of non-filtered smoke to that of the filtered smoke and suitably deliver a taste and aroma of the cigarette. The second object of the present invention is to provide a filter for a cigarette and a filter-tipped cigarette, which can keep the original taste and aroma of the cigarette and provide a milder smoke.
The first object is achieved by a filter for a cigarette, comprising an assembly of: a cylindrical filtering core; a tubular filtering sheath surrounding said core; and, between said core and said sheath, passages spaced circumferentially around said core and extending continuously between open ends at the two ends of the assembly.
When a filter-tipped cigarette using the filter is smoked, part of the smoke of the cigarette passes through the core and the sheath and subsequently is delivered to the smoker. The remaining part of the smoke is directly delivered to the smoker through the axial passages. Since the passages are provided between the core and the sheath, non-filtered smoke can easily reach the smoker""s palate. As a result, even a small quantity of non-filtered smoke enables the smoker to enjoy the original taste and aroma of the cigarette. In other words, the taste and aroma of the cigarette are neither too strong nor too mild, and the smoker can enjoy the aroma and the flavor of the cigarette satisfactorily.
It is preferable that the sheath has a thickness of 1 to 3 mm, the ratio of the core diameter to the thickness of the sheath is 0.7 to 6, and there are 3 to 25 passages.
The axial air-flow resistance of the sheath may be different from that of the core, and the former is preferably higher than the latter. In this case, the quantity of smoke flowing in the core is larger than that flowing in the sheath.
The second object of the invention is accomplished by adding air introducing means to the above-mentioned filter. Ventilation air is introduced into the passages through the sheath and dilutes the smoke flowing in the passages so that the filter will provide the smoker a milder smoke.
The passages may be provided by longitudinal grooves at the outer peripheral surface of the core and/or the inner peripheral surface of the sheath.
When the core has the longitudinal grooves, these may be provided by thermoforming the outer peripheral surface of the core or using a corrugated wrapper or a tubular element at the outer peripheral surface of the core; the inner peripheral surface of the sheath may be formed by thermoforming the inner peripheral surface of the sheath or using an outer wrapper surrounding the core. In this case, the passages are defined between the longitudinal grooves of the core and the inner peripheral surface of the sheath. Air permeability may be imparted to both the inner and outer peripheral surfaces of the sheath so that ventilation air flows radially into the sheath and then into the passages.
When the sheath has the longitudinal grooves, these may be provided by thermoforming the inner peripheral surface of the sheath or using a corrugated wrapper or a tubular element at the inner peripheral surface of the sheath; the outer peripheral surface of the core may be formed by thermoforming the outer peripheral surface of the core or using a wrapper surrounding the core. In this case, the passages are defined between the outer peripheral surface of the core and the longitudinal grooves of the sheath. Air permeability may be imparted to both the inner and outer peripheral surfaces of the sheath, or air permeability may be imparted to the outer peripheral surface of the sheath and openings formed in the sheath in communication with the longitudinal grooves; in either this case, the ventilation air passes radially into the sheath from outside and then into the passages.
Using a cylindrical corrugated wrapper between the sheath and the core may form the passages between the corrugated wrapper and the sheath and between the corrugated wrapper and the core. In this case, the corrugated wrapper may or may not have air permeability.
The passages may be formed in a tubular element which is arranged between the core and the sheath. Air permeability may be imparted to the inner and outer peripheral surfaces of the sheath, with openings in the tubular element connecting the sheath to the passages.
The passages may have a total cross-sectional area of 1 to 3 mm2. In this case, a desirable amount of non-filtered smoke flows in the passages.
The filter may include a cylindrical tip element, which may comprise a filter material. The tip element may have a length from 2 to 20 mm, which is correspondingly 8 to 60% of the overall length of the filter, and an axial air-flow resistance of 80 or less mmH2O/25 mm. The tip element makes it easier to adjust the axial air-flow resistance of the whole filter.
The core and the sheath may be made from different materials or the same material. The filter material is preferably tow of cellulose acetate.